I just looked at the rear picture on your other thread and I THINK I know exactly what you're refering to now. I have the same issue as well and I'm curious if there's a solution. Even with my Keep Faces Setting Checked, I still get those extra faces when I extrude inward.
Edit: or outward on an adjoining face.
Don't be satisfied with what you can do but rather strive to do the things you can't do!
Exceed Expectations!